FAQs

What does SDCP stand for?  

Spatial Data Cooperative Program

 

What data falls under the Spatial Data Cooperative Program?  

Survey-grade orthophotography, LiDAR, derivative products (contours, planimetric data,  landuse/landcover and more) and Nearmap subscription services.

How does the cooperative purchasing process work?

Each year before any data is acquired, NCTCOG coordinates with local public agencies and other entities to determine their need for spatial data.  Based on participant interest the project scope and deliverables are defined. Projects can range in size from a few cities to covering the entire 12,800-sq. mile NCTCOG region and beyond.  Spatial projects are coordinated on an annual basis, but the pricing is not always the same.  

Odd-year Projects - The process of coordinating projects in an odd-year (2007-2023) begins early in the previous year so that cooperative pricing can be calculated based upon the amount of early interest.  This involves two signup forms - a not-to-exceed interest form & a final commitment form. These projects include several counties or more and are heavily discounted (bulk & volume discounting).  This pertains to ortho & LiDAR projects and occasionally derivative projects (if they happen to get big enough).

Even-year Projects - projects are coordinated in even-years for any entity that requests data.  Pricing for these projects is typically higher than in odd-years, because only bulk discounting is available.  Occasionally an even-year project will have enough participants to become a true "cooperative" project.

 

What are the two types of cooperative discounting?

Bulk discounting - cost based upon total square mileage that is negotiated with the chosen vendor.  
Volume discounting - discounts realized as more entities buy-in to a project and there are overlaps in purchase area.

What is leaf-off?

Leaf off is the period between mid-November and mid-March in North America when the leaves have fallen and visibility on the ground is the best.  This is an optimal time for flying orthophotography and LiDAR.

 

What is a corridor?

A corridor is an AOI that follows a path, road, utility (or any) right-of-way.  Due to their unusually narrow shape, corridors require specialized flight plans and 20%-25% more ground control and are thereby more expensive than traditional AOIs.

 

What is an orthophotograph?

An aerial photograph or satellite imagery geometrically corrected ("orthorectified") such that the scale is uniform: the photo or image follows a given map projection. Unlike an uncorrected aerial photograph, an orthophoto can be used to measure true distances, because it is an accurate representation of the Earth's surface, having been adjusted for topographic relief, lens distortion, and camera tilt.  (Wikipedia)
 

 

What map projection is the spatial data in?  

NAD 83 State plane, Zone 4202

 

What does LiDAR stand for?  

Light Detection & Ranging.  It is a method of calculating surface elevation that measures distance to a target by illuminating that target with a pulsed laser light, and measuring the reflected pulses with a sensor.

 

How do I place an order online?

Spatial data can be purchased online at the DFWMaps Marketplace.

What is a tile and how big are they?

In order to manage the data efficiently, the data from the flyover is separated into tiles. The tiles are imported into mapping software and mosaicked (pieced) together so they appear as one seamless image on DFWmaps.com. Each tile is 3,000 feet wide by 2,000 feet high.    The tiles are now used for all  SDCP program data.

 

How is the order delivered?

Data is delivered by FTP within 1-3 business days.  

 

If I've purchased data, can I share it with a consultant?  

Yes, you can share purchased data with consultants who are working with you on a project, as long as you sign and return a contractor's licensing agreement to sbroyles@nctcog.org.   Click here for a copy of the CLA. 

 

What is the graphic format of the aerial photography? 

TIFF (Tagged Image File Format)
MrSID (Multiresolution Seamless Image Database)
ECW (Enhanced Compression Wavelet) - only at the participants request

 

What is a .tiff?

A .tiff is a graphic image, much like a .bmp or .jpeg which includes assigned geographic coordinates either embedded or in a separate world file (.tfw).   Rather than lay on top of one another, the positional information in the TIFF allows them to lay side by side.

 

What is resolution?

Resolution is the size of each pixel in the graphic file. Much like a television screen, aerial photography is a collection of small boxes, or pixels, each having an assigned color. Together the pixels make up an aerial photo. The smaller the pixel the more precise (clear) the orthophoto, however the file size and cost increase with the resolution.

 

What is the appx. file size for a tile? 

3 inch = 280 MB 
6 inch = 71.5 MB 
1 foot = 17.9 MB 
2 foot = 4.5 MB 
4 foot = 1.1 MB 
8 foot = 280 KB

 

How can I view specifications and/or download samples? 

Specifications and samples can be found on most product pages.

• Orthophotography
• LiDAR
• Derivative Products

 

Can aerial photography be certified for legal purposes?

An aerial image can be certified as a NCTCOG product only. Certification costs $50 per item and must be done in person at NCTCOG by a notary public. Contact Shelley Broyles at sbroyles@nctcog.org for more information.  To certify the accuracy of the aerial image, contact the company which flew the aerials (see below).

 

What vendors have you contracted with?

2001 - Vargis, LLC
2003 - Pixxures Inc. and Dallas Aerials Surveys Inc. 
2005 - 2009 - Bohannan Huston
2011 - Sanborn
2013 - 2023 - Woolpert
2017- 2022 - Fugro
2023 - NV5

 

What time of year is the spatial data acquired? 

Leaf-off season.  Aerial photography has historically been flown in January through March, when the visibility of ground features is best.  Due to increased restrictions by DFW ATC, leaf-off projects flown after 2023 will begin in mid-November/December to maximize the flight window.  Vendors can fly imagery leaf-on at an entities request.

 

Are the street names that appear on DFWmaps.com on the aerial photography? 

No, street names are not included on NCTCOG aerial photography.  To view the streets you can download streets and other basemap layers from our Open Data site and overlay them on the orthophotography. 

 

If you are unable to find the answer to your question, send us an email.